FIG. 1. Conventional radio cellular systems include many switches and many individual (non-tunable) duplexers. FIG. 1 illustrates a conventional multi-band system with amplifiers, band switches, duplexers, an antenna T/R (Transmit Receive) switch, and an antenna.
In conventional radio cellular systems that operate in multi-modes and multi-bands (such as 3G, 4G, and/or 5G systems), there are many duplexer related components. These components include T/R (transmit/receive) switches such as PA (power amplifier) band switches and antenna band switches. These components are growing in numbers and undesirably increasing the total solution cost and size.
Specifically, FIG. 1 illustrates a conventional system including: amplifiers (AMP 2 and AMP4); band switches (SW2 and SW4); duplexers module (DMOD) including duplexers (D17, D8, D5, D13, D2, D1, and D4); an antenna T/R (Transmit/Receive) switch SW6; and a main antenna ANT. For the sake of clarity and conciseness, many other elements (such as a diversity antenna and related circuitry) are not shown in FIG. 1. Also, the wiring for received signals exiting the duplexer is not shown.
Beginning with low band elements, low-band amplifier AMP2 receives a voltage VA2IN and then outputs an amplified voltage VA2OUT. Low-band switch SW2 receives VA2OUT, and selectively outputs one of: V17, V8, V5, and V13.
High-band amplifier AMP4 receives a voltage VA4IN and outputs an amplified voltage VA4OUT. High-band switch SW4 receives VA4OUT and then selectively outputs one of: V2, V1, and V4.
In a transmit mode, duplexers module DMOD receives a selected voltage (V17, V8, V5, V13, V2, V1, or V4), processes the selected voltage through a corresponding duplexer (D17, D8, D5, D13, D2, D1, or D4 respectively), and outputs a duplexed voltage (VD17, VD8, VD5, VD13, VD2, VD1, or VD4 respectively.
Remaining in transmit mode, antenna T/R (transmit/receive) switch SW6 receives one or more duplexed voltages (VD17, VD8, VD5, VD13, VD2, VD1, or VD4), selects one of these received duplexed voltages, and outputs the selected voltage as VANT to main antenna ANT.
In a receive mode, signals flow from right to left. Main antenna ANT receives a signal as VANT, antenna T/R switch selectively outputs VANT as one of VD17, VD8, VD5, VD13, VD2, VD1, or VD4 towards a corresponding duplexer (D17, D8, D5, D13, D2, D1, or D4 respectively). For example, if duplexer D17 is selected, then the received signal VANT is transmitted through antenna T/R switch SW6 and then towards duplexer D17 as VD17. Duplexer D17 receives the received signal VD17, and then outputs a duplexed received signal (not shown). The duplexer generally performs filtering that is specific for the band in which the duplexer is operating.
FIG. 2(a). FIG. 2(a) is a conventional dual hybrid tunable duplexer with intra-filters that reflect RX signals and pass TX signals, illustrating the paths from a power amplifier to an antenna. The hybrid structures in FIG. 2(a) are 90 degree hybrid structures with a −3 dB power split on the quadrature ports. These hybrids are also known as 90 degree Hybrid couplers or Quadrature Couplers.
Specifically, FIG. 2(a) illustrates power amplifier AMP6 outputting signal V20 for transmission. Hybrid HYB2 receives signal V20 and splits this signal into two “half power” signals: V22 exiting the top right with no phase shift (an “in-phase output”), and V23 exiting the bottom right with 90 degree phase shift (a “quadrature component”). Thus, hybrid HYB2 simultaneously provides a 3 dB power split into two signals (half power to the upper right, and half power to the lower right), and a 90 degree phase shift to one of the signals (to the lower right).
Tunable filter TF2 receives V22 (the upper signal, or “in-phase output”), and transmits almost all of this signal as V24 (due to low reflectivity Γ in the TX band, and high reflectivity Γ outside of the TX band). For example, Tunable filter TF2 may be a band pass filter centered at the transmit frequency.
Tunable filter TF4 receives V23, and transmits almost all of this signal as V25 (due to low reflectivity Γ in the TX band). In one embodiment, tunable filters TF2 and TF4 are identical.
Hybrid HYB4 receives V24, shifts it 90 degrees, and send it out the antenna port Port2 to the antenna ANT. Additionally, HYB4 receives V25, and sends it out Port2 without any additional shifting. Now, these two half power signals have each been shifted 90 degrees, and they will add (not cancel) at Port2. Thus, the antenna ANT receives combined signal VANT substantially equivalent to the entire V20 shifted 90 degrees, and with out of band portions of the signal having been filtered or reflected (high Γ RX) out.
In summary, HYB2 splits the TX signal into two halves, while shifting the lower half by 90 degrees. The second hybrid HYB4 combines the split signals, while shifting the upper half by 90 degrees. Overall, the antenna ANT receives combined signal VANT that is substantially equivalent to the entire V20 shifted 90 degrees. Additionally, tunable RX filter TRXF2 and isolator ISO2 are discussed below.
During transmission, hybrid or “quadrature” coupler HYB4 typically provides 20 to 30 dB of isolation between receiving RX port 3 and transmitting antenna port 2.
FIG. 2(b). FIG. 2(b) illustrates isolation at the receiver port caused by the second hybrid coupler. Specifically, as discussed above, hybrid HYB4 receives signal V24 (a half power, un-shifted, filtered, transmission signal). V24 is transmitted directly to V26 without any additional shifting.
Additionally, hybrid HYB4 receives signal V25 (a half power, 90 degree shifted, filtered transmission signal). V25 is transmitted to V26 with an additional 90 degree shift, creating a half power, 180 degree shifted, filtered transmission signal. Thus, V26 combines a half powered, un-shifted, filtered transmission signal with a half power, 180 degree shifted, filtered transmission signal, and these two signals ideally cancel out because they are equivalent in magnitude but 180 degrees out of phase. Thus, V26 is near zero, illustrating very high isolation between the transmitted output VANT and any signal leaking out as V26. In practice, these combined signals do not perfectly cancel (due to mismatching), but they do provide approximately 20 dB to 30 dB of cancellation (20 to 30 dB lower power than the transmission signal VANT).
FIG. 2(c). FIG. 2(c) illustrates reflections from the tunable filters directed towards the isolation port. Tunable filter TF2 reflects (leftward) any out of band portions of the received half power un-shifted transmission signal V22 (due to high Γ RX). Hybrid HYB2 shifts this upper reflected signal by 90 degrees and sends the shifted reflected signal (downward and to the left) to the isolation port Port4.
Tunable filter TF4 reflects (leftward) any out of band portions of the received half power 90 degree shifted transmission signal V23 (due to high Γ RX). Hybrid HYB2 does not shift this lower reflected signal any more, while sending this reflected signal (to the left) to the isolation port Port4.
Isolation port resistor ISO4 absorbs both of these (out of band, undesired) reflected signals, in order to avoid these reflected signals being problematically reflected back into the hybrids.
FIG. 2(d). FIG. 2(d) illustrates receiving an un-tuned signal. An un-tuned signal RX is received at antenna ANT, and accepted by hybrid HYB4 at Port2. A half power 90 degree shifted un-tuned signal RX is output (upper left) towards filter TF2. Simultaneously, a half power un-shifted un-tuned signal RX is output (lower left) towards filter TF4.
FIG. 2(e). FIG. 2(e) illustrates reflecting and tuning the received signal. Filter TF2 reflects the half power, 90 degree shifted un-tuned signal RX to the upper left of hybrid HYB4. HYB4 passes this signal (without additional shifting) towards tunable RX filter TRXF2.
Further, filter TF4 reflects the half power, un-shifted, un-tuned signal RX to the lower left of hybrid HYB4. Hybrid HYB4 passes this signal (while adding a 90 degrees shift) towards tunable RX filter TRXF2.
Exiting the top right of hybrid HYB4, these two half power signals (now each shifted 90 degrees) are combined into a whole power signal shifted 90 degrees V26. Tunable filter TRXF2 may be tuned to a specific band, and thus may pass VRXOUT in a selected specific band, while filtering out portions of the received signal that are in other bands.
FIG. 3(a). FIG. 3(a) is a second type of conventional dual hybrid tunable duplexer, with intra-filters that pass RX signals and reflect TX signals, illustrating the paths from a power amplifier to the intra-filters.
Specifically, FIG. 3(a) is a different configuration of the same elements shown in FIG. 2(a), except that the intra-filters (the tunable filters located between the hybrids) now pass (instead of reflect) RX signals, and reflect (instead of pass) TX signals. Power amplifier AMP8 sends a transmission signal TX to Port1 of hybrid HYB8. Hybrid HYB8 sends a half-power, un-shifted TX signal to tunable filter TF6, and sends a half-power, 90 degree shifted TX signal to tunable filter TF8. In one embodiment, tunable filters TF6 and TF8 are identical.
FIG. 3(b). FIG. 3(b) reflects transmission signals by the “intra-filters” located between the hybrids. The split signals from the previous figure are each reflected. Specifically, the half power, un-shifted signal is reflected by tunable filter TF6 (due to high Γ TX). Any out of band portions of this signal are passed by the tunable filter. In other words, the reflected signal has been filtered to be in a selected transmission band. Hybrid HYB8 receives this reflected signal at the upper left, and sends it towards the antenna while shifting 90 degrees (resulting in a half power, 90 degree shifted, filtered signal at Port2).
Tunable filter TF8 receives a half-power, 90 degree shifted, unfiltered signal from hybrid HYB8, and reflects a filtered portion of this signal back towards hybrid HYB8 (due to high Γ TX). Hybrid HYB8 passes (receives at the lower left port and sends out the lower right port of the hybrid) this reflected signal (without any additional phase shift) towards the antenna ANT at Port2.
These two half-power, 90 degree shifted, filtered signals are combined at Port2 to create a full-power, 90 degree shifted, filtered signal TXOUT.
FIG. 3(c). FIG. 3(c) illustrates that the RX noise is cancelled. Tunable filters TF6 and TF8 passes (low Γ RX) portions of TXIN that are outside of a selected TX band. These transmitted noise signals pass through hybrid HYB6. The lower noise signal is shifted 90 degrees (for a second time) by HYB6, resulting in 180 degree shifted signal exiting at Port3. The upper signal is passed by HYB6 without any shifting to Port3. These two noise signals effectively cancel at Port3 (RXOUT equals about zero) because one of the noise signals has been shifted 180 degrees, and the other has not been shifted.
Somewhat similar to the above discussion of FIGS. 2(a)-(e), FIGS. 3(a)-(c) provide substantial isolation between full power, 90 degree shifted, filtered output TXOUT relative to noise RXOUT. Isolation resistor ISO4 performs a function (terminating reflections) similar to isolation resistor ISO2 in FIG. 2, as discussed above.
The above conventional architectures suffer because the isolation from the transmit port Port1 relative to the receive port Port3 is a function of antenna load changes. The antenna load changes may be characterized by an antenna VSWR (Voltage Standing Wave Ratio). Thus, conventional architectures suffer from degraded isolation whenever VSWR changes, and an antenna load can often change by a factor of 10 (up to 10:1 VSWR).
Additionally, if the antenna is not almost perfectly matched, then the performance of the conventional architectures degrades. For example, if the dual hybrid has an impedance of 50 ohms, and if the antenna does not have an impedance of 50 ohms, then the antenna is mismatched at the antennal port Port2 of the dual hybrid. Further, antenna load changes may change the impedance of the antenna during operation. Conventional architectures cannot solve these problems.